I made all my furniture and floor from scratch. I had the pop-top and Reimo 3000 sliding bed fitted. The Reimo has to be done by the qualified fitter. Everything else I did myself.
If I was doing it again, I would learn CAD properly, and have the ply panels CNC cut. I would also fit the roof myself, then I could be extra fussy about keeping everything clean and rock solid.
In terms of elapsed time, the van arrived in September, and it was more or less done by Easter.
The design and research time was a significant part of the effort, which would be much quicker second time around.